In recent years, SiP (System in Package) systems for performing sophisticated signal processing, each comprising a plurality of integrated semiconductor circuits (hereinafter referred to as “chips”) encapsulated in a single package, have been used in a wide range of applications. To meet the growing demand for higher SiP functionality, the number of chips encapsulated in one package is on the increase. However, the large number of chips encapsulated in one package have posed problems in that it is difficult to ensure signal transmission between the chips and the package tends to have an increased volume.
In view of the above problems, there has been developed a packaging apparatus which vertically stacks chips having signal transmission paths perpendicular to the upper surfaces thereof in the form of an electrically conductive material that fills through holes defined in the chips, thereby making packaging means such as wire bonding means unnecessary.
Since the above configuration makes it possible to perform direct signal transmission between the stacked chips, a wider bandwidth can be achieved and the SiP can be reduced in volume.
To carry out another packaging method, there has been developed a semiconductor device comprising chips having electromagnetic induction coils disposed thereon and stacked in a direction perpendicular to the upper surfaces of the chips, for performing signal transmission based on an electromagnetic coupling of the electromagnetic induction coils (see, for example, JP No. 1995-221260 A, JP No. 1996-236696 A, and document: Noriyuki Miura, et al., “Analysis and Design of Transceiver Circuit and Inductor Layout for Inductive Inter-chip Wireless Super-connect”, IEEE 2004 Symposium on VLSI Circuits Digest of Technical Papers, pp. 246-249 (2004)).
FIG. 1 is a view showing a first form of a general semiconductor device used for signal transmission.
The semiconductor device shown in FIG. 1 includes first circuit chip 100 and second circuit chip 101, having respective electromagnetic induction coils 102, 103 and respective ferromagnetic films 104, 105.
FIG. 2 is a view showing a second form of a general semiconductor device used for signal transmission.
The semiconductor device shown in FIG. 2 comprises three chip layers.
Transmitter S on chip layer Ln has input terminal 201 and output terminals 202, 202′, and voltage U201 is applied to input terminal 201. Receiver E on chip layer Ln+x has input terminals 203, 203′ and output terminal 202, and voltage U204 is applied to output terminal 204.
FIG. 3 is a view showing a third form of a general semiconductor device used for signal transmission.
The semiconductor device shown in FIG. 3 comprises memory chips 300, 301, analog chip 302, and logic chip 303 which are stacked together. Electromagnetic induction coil 304 is disposed on memory chip 300, electromagnetic induction coil 305 on memory chip 301, electromagnetic induction coil 306 on analog chip 302, and electromagnetic induction coil 307 on logic chip 303.
The semiconductor devices shown in FIGS. 1 through 3 include electromagnetic induction coils and signal devices disposed on the chips and stacked in a direction perpendicularly to the upper surfaces of the chips and secured in place by adhesive layers or the like.
It is assumed that a coil and a signal device which are disposed in a lower position are used to transmit a signal and a coil and a signal device which are disposed in an upper position are used to receive a signal. The transmission coil is supplied with a current from the signal device in a direction depending on the transmission signal. For example, if a current signal directed clockwise is representative of “1”, then the transmission coil generates magnetic fluxes in a downward direction through the reception coil. The reception coil induces a current due to the magnetic fluxes directed therethrough. At this time, the induced current has the same direction as the current supplied to the transmission coil. The induced current or an electric signal such as a voltage converted therefrom is observed by the signal device, thereby performing signal transmission.
If a current signal representative of “0” is to be sent, a current is supplied counter-clockwise, a direction opposite to the direction of the current representative of “1” is supplied, thereby performing signal transmission.
Generally, the signal transmission based on an electromagnetic coupling of electromagnetic induction coils results in a smaller area being occupied by I/O parts than a packaging configuration with area bumps, and makes it possible to produce more highly integrated circuits.
However, the above signal transmission structure is only able to perform signal transmission between chips that are stacked perpendicularly to the upper surfaces of the chips, and is unable to perform signal transmission parallel to the upper surfaces of the chips. Consequently, the above technology is not available in applications where chips cannot be stacked perpendicularly to the upper surfaces thereof due to the heat generated by the chips operation.
Devices other than SiP systems also require signal transmission between chips arrayed parallel to the upper surfaces thereof. For example, one such device is used in a process of inspecting a wafer before it is diced into chips in the fabrication of LSI circuits (wafer level inspection process). Chips on a wafer are made independent of each other by scribe lines that are grounded. When the wafer is diced into the chips, the wafer is cut along the scribe lines. If there are connections extending across the scribe lines, then a problem such as short circuits will arise when the wafer is diced. Consequently, the chips cannot be interconnected by connections extending across the scribe lines. In the wafer level inspection process, therefore, inspection data between the chips cannot be shared by the single wafer, but have to be shared by an external device such as a probe card or the like. As a result, the necessary connections tend to occupy a large area.